Positive displacement dispenser and method for dispensing discrete amounts of liquid

ABSTRACT

A dispenser for applying small amounts of liquid to a substrate. The dispenser includes a dispenser body, an actuator in the dispenser body, and a dispensing element including a dispensing element body removably coupled to the dispenser body. A valve stem is mounted for reciprocating movement within the dispensing element body. Additional aspects include a deformable valve seat, a deformable and resilient valve stem tip and a method of applying liquid in discrete amounts to a substrate.

TECHNICAL FIELD

The present invention generally relates to liquid dispensers, such aspositive displacement pumps and jetting dispensers, designed toaccurately dispense discrete amounts of liquid.

BACKGROUND

Various types of industrial liquid dispensing applications haverequirements related to dispensing small, discrete amounts of liquidwhile achieving high degrees of accuracy, uniformity and/orrepeatability during successive and often rapid dispense cycles.Positive displacement pumps are used to achieve at least some of thesepurposes. However, various applications require dispense amounts, cycletimes and other process parameters that typical positive displacementpumps cannot meet. On the other hand, apparatus that can meet theseother process parameters may not dispense with the required accuracy,repeatability and/or uniformity. For example, dispensers may utilizeelements that are acted upon by air pressure or mechanical devices, suchas stepper drives, at a location remote from the point of application.Under these circumstances, the deposition amount or volume of dischargedliquid can vary depending on a number of factors. This may require thatthe user continually adjust system settings in order to maintain uniformapplication rates. Even so, the desired or required degree of accuracyand uniformity may not be achieved. In addition, the size of a desiredliquid deposition is often very small, such as on the order of 10⁻⁷ in.³or less, and this can create process control issues. Also, many of thematerials that are used in industry are curable or hardenable materials,such as epoxies, which can create additional challenges related tomaintenance.

Various forms of jetting dispensers are known and have been usedsuccessfully to dispense small amounts of viscous liquids with a highdegree of accuracy, uniformity and repeatability. Challenges that remainwith regard to jetting technology include the challenge of maintainingthe inner components and passages clear of residual liquid materialbetween dispense operations so that repeated use of the jettingdispenser can occur without any negative effects of cured or hardenedmaterial within the device. In addition, there are times when liquidsatellite formation is a problem. This involves the formation ofadditional small amounts of the liquid around the dispensed amount.Satellite formations and/or undesired atomization may negatively affectthe deposition pattern that is desired on the intended substrate.Finally, leakage of liquid from the outlet of a jetting dispenserbetween dispense cycles can be a problem.

It would therefore be desirable to provide a liquid dispenser thataddresses concerns such as those mentioned above, and can lessen theneed to clean various components and passages, lessen satelliteformation and atomization, and prevent leakage of liquid from thedispensing outlet between dispense cycles.

SUMMARY

In one illustrative embodiment, a dispenser for applying small amountsof liquid to a substrate is provided and generally comprises a dispenserbody, an actuator in the dispenser body, and a dispensing element. Thedispensing element includes a dispensing element body removably coupledto the dispenser body and a valve stem mounted for reciprocatingmovement within the dispensing element body. The dispensing element bodyfurther includes a liquid chamber. The valve stem includes a tip mountedfor reciprocating movement within the liquid chamber between open andclosed positions. The dispensing element further includes a valve seatengaging the valve stem tip in the closed position, as well as a liquiddispensing outlet and a liquid supply passage. The valve seat ispositioned between the liquid chamber and the liquid dispensing outlet.The liquid supply passage communicates with the liquid chamber. Thevalve stem further includes an opposite end relative to the tip. Theopposite end of the valve stem is adapted to be operatively coupled tothe actuator when the dispensing element is coupled to the dispenserbody. Because the dispensing element is removable from the dispenserbody and includes the various passages for the liquid, and also includesthe valve stem, the dispensing element may be discarded and replaced bya new dispensing element as necessary to avoid maintenance and/orcontamination concerns associated with residual liquid.

The dispensing element body in various embodiments may have additionalfeatures. For example, the dispensing element body includes an airsupply passage and an air discharge passage communicating with the airsupply passage. The air discharge passage is positioned adjacent to theliquid dispensing outlet and is adapted to discharge a pressurized aircurtain surrounding the liquid as the liquid is dispensed from theliquid dispensing outlet. This feature can lessen the occurrence ofliquid atomization and/or effect of satellite liquid formations aroundthe liquid discharge from the outlet. The dispensing element bodyfurther includes a connector element adapted to couple with a containeror reservoir of the liquid, such as a removable container typically usedwith syringe-type dispensers. The dispenser body further includes anopening adapted to receive an outlet portion of the container and theconnector element is positioned in the opening when the dispensingelement body is coupled to the dispenser body. The dispensing elementbody may comprise a plastic material for disposability and/or otherpurposes.

The valve seat, in additional or alternative embodiments, can furthercomprise a separate element carried by the dispensing element body. Inone embodiment, the valve seat is malleable and deformed by the valvestem tip in the closed position. The plastic material of the dispensingelement body can also be deformed as the valve stem tip engages theoverlying malleable valve seat. The combined deformation of the valveseat and the underlying material of the dispensing element body achievesat least two purposes. It can damp the impact of the valve stem tipagainst the valve seat and also increase the amount of contact betweenthe valve stem tip and the valve seat. Specifically, a concave area ofsealing contact is formed between the valve stem tip and the valve seat.This increases the sealing effect of the valve stem tip. The dampingaction can reduce the formation and/or amount of liquid satelliteformation or atomization of the dispensed liquid. The valve seat furthercomprises a cone shaped portion for engaging the valve stem tip and anelongate dispensing tip portion including a liquid dispensing passagecommunicating with the liquid dispensing outlet. A securing cap isremovably coupled to the dispenser body and secures the dispensingelement to the dispenser body. The securing cap includes an opening thatreceives the elongate dispensing tip portion of the valve seat. Theopening further communicates with the air discharge passage and isconfigured to direct the pressurized air curtain in surrounding relationto the liquid as the liquid is dispensed from the liquid dispensingoutlet.

The dispensing element further comprises a dynamic seal engaged with thevalve stem. The dynamic seal prevents the escape of liquid from theliquid chamber during operation of the dispenser. The valve stem extendsthrough the dynamic seal such that the opposite end of the valve stem ispositioned outward of the liquid chamber and in operative engagementwith the actuator. A spring element is coupled with the dispensingelement body and the valve stem for biasing the opposite end of thevalve stem into proper position, such as in engagement with theactuator.

In another alternative or additional aspect of the invention, adispenser for applying small amounts of liquid to a substrate isprovided and generally includes a dispensing portion, an actuatorportion, and a valve stem mounted for reciprocating movement within thedispensing portion. The dispensing portion further includes a liquidchamber and the valve stem includes a tip mounted for reciprocatingmovement within the liquid chamber between open and closed positions.The dispenser further includes a valve seat in the dispensing portion.The valve stem tip engages the valve seat in the closed position. Thedispensing portion further includes a liquid dispensing outlet and aliquid supply passage. The valve seat is positioned between the liquidchamber and the liquid dispensing outlet. The liquid supply passagecommunicates with the liquid chamber. The valve stem is operativelycoupled to the actuator such that the actuator is capable of moving thevalve stem between the open and closed positions. The valve seat isformed by a first, malleable material in abutting contact with a second,deformable material. The first and second materials are deformed whenthe valve stem moves to the closed position. This damps the impact ofthe valve stem tip against the valve seat and forms an area of sealingcontact between the valve stem tip and the valve seat.

The first, malleable material can further comprise a metal, while thesecond, deformable material may further comprise a plastic material. Forexample, the metal material may be a thin and ductile stainless steelsheet material and the plastic may be polypropylene. The valve stem tipmay be rounded such that upon impact when reaching the closed position,the valve stem tip plastically deforms the metal and the underlyingplastic to create an annular, concave ring in the valve seat. Thisannular concave ring forms an effective sealing area, while alsoproviding a damping effect.

In another alternative or additional aspect, the dispenser may begenerally constructed as discussed above. This embodiment employs avalve stem tip that is formed from a deformable, resilient material. Inthis embodiment, the valve stem tip is deformed against the valve seatwhen the valve stem moves to a closed position. This provides both adamping effect upon impact of the valve stem tip against the valve seatand forms a larger area of sealing contact between the valve stem tipand the valve seat than would otherwise be formed with a rigid valvestem tip and rigid valve seat. In this embodiment, the valve seat may beformed from a rigid material that is not deformed when impacted by thevalve stem tip. The valve stem may further include a main portioncoupled with the tip and formed from a rigid metal, while the tip can beformed from an elastomeric material which deforms in a resilient manner.

A method of applying a small amount of liquid to a substrate during adispense cycle is also provided. The liquid is dispensed from adispenser including a valve stem with a tip, a liquid chamber, a liquiddispensing passage communicating with a liquid dispensing outlet, and avalve seat positioned between the liquid chamber and the liquiddispensing passage. The method includes moving the valve stem tip from aclosed positioned which is engaged with the valve seat to an openposition which is disengaged and spaced from the valve seat. Pressurizedliquid is allowed to flow from the liquid chamber past the valve stemtip and into the liquid dispensing passage. The valve stem tip is thenmoved from the open position to the closed position thereby forcing adiscrete amount of liquid onto the substrate. The valve stem tip ismaintained in the closed position until an initiation of a subsequentdispense cycle. In this manner, liquid from the liquid dispensing outletis prevented from leaking out of the outlet between dispense cycles.

Various additional features and advantages of the invention will becomemore apparent upon review of the following detailed description of theillustrative embodiments taken in conjunction with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a dispenser constructed in accordancewith one illustrative embodiment of the invention.

FIG. 2 is a cross sectional view of the dispenser shown in FIG. 1,generally taken along line 2-2.

FIG. 3 is a bottom perspective view of a dispensing element bodyassociated with the dispenser of FIG. 1.

FIG. 4 is a top perspective view of the dispensing element body shown inFIG. 3.

FIG. 5 is a cross sectional view similar to FIG. 2, but showing anenlarged view of the dispensing portion of the dispenser while ejectinga small amount of liquid.

FIG. 6 is a cross sectional view similar to FIG. 5, but illustrating asubsequent point in the dispensing process.

FIG. 7 is a cross sectional view similar to FIGS. 5 and 6, but furtherenlarged to show details of the valve stem tip and valve seat in theclosed position.

FIG. 7A is a cross sectional view similar to FIG. 7, but illustrating analternative embodiment.

FIG. 8 is a cross sectional view similar to FIG. 5, but illustrating analternative embodiment of the valve stem in the open position.

FIG. 9 is a cross sectional view similar to FIG. 8, but showing thevalve stem of FIG. 8 in the closed position.

FIG. 10 is a cross sectional view similar to FIGS. 8 and 9, butillustrating the valve stem in a transitioning position between the openand closed positions.

DETAILED DESCRIPTION OF THE ILLUSTRATIVE EMBODIMENTS

FIGS. 1 and 2 illustrate a dispenser 10 constructed in accordance withone illustrative embodiment. It should be noted that various spatial anddirectional references, such as horizontal, vertical, upper, lower, etc.are used with regard to describing the drawing figures and that this isdone for convenience and clarity of description only. It will beunderstood that the dispenser 10 may be used in various orientations andmay dispense a variety of liquids having a wide range of viscositiessuch as alcohols with viscosities less than water and epoxy resins withviscosities well above that of water. The dispenser 10 generallycomprises a dispensing portion 10 a and an actuator portion 10 b, andthese portions are associated with a dispenser body 12 in theillustrative embodiment. The dispenser 10 further includes a containeror reservoir 14 of the liquid 15 to be dispensed. The container 14 isremovably coupled to the dispenser body 12. The container 14 includes afirst end 16 and second end 18. The first end 16 is received with anopening 20 and is coupled with a connector 22, as will be describedfurther below. The second end 18 includes an additional connector 24with a fluid fitting 26 for coupling to tubing (not shown). Thecontainer 14 holds the liquid 15 to be dispensed as well as a piston(not shown). The piston is moved to pressurize the liquid 15 byintroducing pressurized air on an upper side of the piston through thefitting 26. The liquid 15 in the container 14 may be under a relativelow pressure of, for example, 10 psi. This exemplary syringe-typecontainer 14 is more fully shown and described in U.S. PatentPublication No. 2007/0287965, the disclosure of which is hereby fullyincorporated by reference herein. As further shown in FIG. 1, a solenoidvalve 30 and associated wiring 30 a is coupled to and extends within thedispenser body 12 and controls pressurized actuation air, as will bedescribed further below. The actuation air is received through a fitting32 and is directed through one or more passages (not shown) leading tothe portion of the solenoid valve 30 contained in the dispenser body 12.An additional fitting 34 (FIG. 2) receives pressurized process air intothe dispenser body 12 also as described further below. For applicationsrequiring heated liquid and process air, the dispenser body 12 containsa cartridge-style heater and resistance temperature detector or RTD (notshown). These may be accessed by removing a cap 36 secured withfasteners 38. The wiring 40 for the heater and RTD is shown in FIGS. 1and 2. It will be appreciated that the dispenser body 12 may be heatedto and controlled at the required application temperature by othersuitable methods instead. The dispenser body 12 is formed from a heatconductive material, such as aluminum.

Referring more specifically to FIG. 2, a dispensing element 50,including a dispensing element body 52, is removably coupled to thedispenser body 12 by a threaded cap 54 received on a threaded extension56 of the dispenser body 12. The dispensing element body 52 includes aliquid chamber 58 and a valve stem 60 having a tip 60 a and mounted forreciprocating movement within the liquid chamber 58 between open andclosed positions. The tip 60 a may be integrally formed with theremainder of the valve stem 60, or may be a separate part secured to theremainder of the valve stem. In this embodiment, the tip 60 a is formedfrom Viton having a Shore A hardness of 50. The closed position is shownin FIG. 2. The dispensing element 50 further comprises a valve seat 62engaging the valve stem tip 60 a in the closed position. The valve seat62, in this illustrative embodiment, comprises an elongate elementhaving a cone or funnel shaped portion 62 a and a tubular dispensing tipportion 62 b integral with and extending from the cone shaped portion. Aliquid dispensing outlet 64 is located at the end of the tubulardispensing tip 62 b. A liquid supply passage 66 is in fluidcommunication with the liquid chamber 58 and also with the connector 22coupled in fluid communication with the container 14. Pressurized liquid15 therefore flows from the container 14 through the connector 22 andthe liquid supply passage 66 into the liquid chamber 58. When the valvestem 60 is in the closed position as shown in FIG. 2, the liquid 15 isprevented from discharging through the outlet 64. It will be appreciatedthat the connector 22 may be part of the container 14 or may be part ofthe dispensing element 50. Respective threads 70, 72 are used betweenthe connector 22 and the dispensing element body 52 for maintaining afluid tight connection.

The dispensing element 50 further includes a valve stem guide element 76and a dynamic seal 78, as well as a spring element 80 and springretainer 82 that is snapfit into a groove 84 proximate an end 60 b ofthe valve stem 60 opposite to the valve stem tip 60 a. The actuatorportion 10 b of the dispenser 10 comprises an actuator 90. The end 60 bof the valve stem 60 is adapted to be moved by the actuator 90. Theactuator 90 is retained by a cap 94 with threads 96 on the outside ofthe cap 94 engaging threads 98 in an opening 100 of the dispenser body12. The cap 94 further includes a adjustment screw 102 and a coil spring104. The coil spring 104 maintains the valve stem 60 in a normallyclosed position. The spring 104 bears against a piston 110 fixedlymounted to an end of an actuating element 112. The actuating element 112includes a cylindrical end portion 114 adjacent to the end 60 b of thevalve stem 60. The end portion 114 slides within a dynamic seal 116mounted in the dispenser body 12 to seal a piston chamber 120 thatreceives the piston 110. Pressurized air is introduced into an airsupply passage 122 from the air fitting 32 by switching the solenoidvalve 30 (FIG. 1). The air is directed to the underside of the piston110 within the piston chamber 120. Introducing air to the underside ofthe piston 110 will raise the piston 110 and the attached actuatingelement 112 against the spring bias of the coil spring or return spring104 thereby compressing the spring 104. This will allow the valve stem60 to move to the open position due to the bias provided by the springelement or coil spring 80 associated with the dispensing element 50while, in this embodiment, maintaining engagement of the upper end 60 bof the valve stem 60 with the lower end 114 a of the actuating element112. In other embodiments, such as when additional closing force isnecessary for dispensing more viscous liquids, the lower end 114 a ofthe actuating element 112 may be spaced from the upper end 60 b of thevalve stem when the valve stem 60 is in the open position. When theactuating air is exhausted from the air supply passage 122 and thepiston chamber 120 on the underside of the piston 110 by again switchingthe solenoid valve 30 (FIG. 1), the return spring 104 will force thepiston 110, the attached actuating element 112 and the valve stem 60,which is engaged with the end of the actuating element 112, downwardsuch that the valve stem tip 60 a engages the valve seat 62. It will beappreciated that other actuators may be used instead, such as pistonsoperated in both directions by pressurized air or electric actuators.

The adjustment screw 102 is used to set the stroke length of the valvestem 60 which may, for example, be 0.010″ to 0.020″. Specifically, theadjustment screw 102 is rotated and driven downward until the valve stemtip 60 a stops against the valve seat 62. Then, the screw 102 is rotatedin the opposite direction and backed out of the cap 94 to achieve thedesired stroke length. When pressurized actuation air is introduced intothe supply passage 122 and the piston chamber 120, the piston 110 andattached actuating element 112 will be moved upwardly until an end 112 bof the actuating element 112 engages the bottom 102 a of the adjustmentscrew 102. Therefore, this will set the maximum stroke of the valve stem60 which will raise or lift off of the valve seat 62 by the samedistance.

The piston 110 includes a wiper 110 a that engages the internal wall 120a of the cylindrical piston chamber 120 in a dynamic sealing fashion toensure that the pressurized actuating air is sealed between the wiper110 a and the dynamic seal 116 mounted within the dispenser body 12 andaxially aligned with the valve stem 60 and the actuating element 112. Asfurther shown in FIG. 2, an air supply passage 140 for supplyingpressurized process air is also provided in the dispenser body 12 andreceives air through the fitting 34. Passage 140 communicates with apassage in the form of a groove 142 on the upper side of the dispensingelement body 52. This groove 142 is in fluid communication with anotherair passage 144 and, ultimately, with an opening 146 in the cap 54 tocreate a curtain of pressurized air in surrounding relation to thedispensing tip 62 b, as will be described further below. The opening 146has a diameter sufficiently larger than the outer diameter of thedispensing tip 62 b so as to create the desired air annulus anddischarged air curtain. For example the air annulus may be approximately0.005″.

FIGS. 3 and 4 illustrate the dispensing element body 52 in greaterdetail, including the various process air passages. Referring now toFIGS. 2-4, the air supply groove 142 communicates and connects with anannular groove 150 in the dispensing element body 52 that surrounds theguide element 76. This annular groove 150 communicates with the verticalair supply passage 144 which, in turn, communicates with an annulargroove 152 on the underside of the dispensing element body 52 insurrounding relation to an opening 153 that receives the dispensing tip62 b of the valve seat 62 in a sealing manner, such as by beingadhesively secured therein. The annular or ring shaped groove 152communicates with the central opening 146 (FIG. 2) via three connectinggrooves 154 a, 154 b, 154 c. Grooves 152, 154 a, 154 b, 154 c on theunderside of the dispensing element body 52 as well as grooves 142, 150on the top of the dispensing element body 52 form passages when the cap54 is tightly secured to the dispenser body 12 as shown in FIG. 2. Inthis regard, the bottom surface 12 a of the dispenser body 12 closes theopen, upper sides of the grooves 142, 150, and the inner surface 54 a ofthe cap 54 closes the open, lower sides of the grooves 152, 154 a, 154b, 154 c. The pressurized process air is directed from the annulargroove 152 and connecting grooves 154 a, 154 b, 154 c to the opening 146in the cap 54 that receives the dispensing tip 62 b (FIG. 2).

FIGS. 5 and 6 illustrate the operation of the valve stem 60 and the useof the process air while dispensing a small amount of liquid 15, such asan epoxy or other liquid of greater or lesser viscosity. FIG. 5illustrates both the initial and ending positions of the valve stem tip60 a during a dispense cycle. As shown in FIG. 6, the valve stem 60 isinitially moved to disengage the valve stem tip 60 a and space the valvestem tip 60 a from the valve seat 62 as shown. This allows the viscousliquid 15, which is under pressure, to fill any void that is within theliquid passage 160 communicating with the outlet 64. As previouslydescribed, the valve stem 60 is raised or disengaged from the valve seat62 by introducing pressurized actuating air into the piston chamber 120(FIG. 2). To dispense a small amount of the liquid 15, such as a drop162, the actuating air is exhausted from the piston chamber 120 and thereturn spring 104 and attached actuating element 112 force the valvestem 60 downward such that the tip 60 a engages the valve seat 62 andforces a discrete and accurate amount of the liquid 15 onto thesubstrate 164. During the dispense cycle, process air is dischargingthrough the opening 146 of the cap 54 surrounding the dispense tip 62 bto create a curtain of air that contains and/or reduces the formation ofany small amounts of satellite liquid associated with the drop 162. Atthe end of the dispense cycle, the valve stem tip 60 a is maintained inthe closed position as shown in FIG. 5 such that, between dispensecycles, the liquid 15 in the passage 160 communicating with the outlet64 is not under pressure that would potentially cause leakage from theoutlet 64 between the dispense cycles. The dispenser 10 may be operatedto rapidly dispense small amounts of liquid 15, on the order of about0.02 microliter to about 0.1 microliter at a rate of 100 Hz or less,although these parameters may be adjusted depending on the applicationand the specific embodiment of the invention practiced.

As best shown in FIG. 7, the valve stem tip 60 a engages the valve seat62 in the closed position and forms plastic deformations 170, 172 in acone shaped portion 62 a of the valve seat 62 and the underlyingmaterial of the dispensing element body 52. The valve seat 62 is formedby a deep drawing process from a thin and malleable metal, such asductile stainless steel having a thickness between about, for example,0.0015″ and about 0.0025″. The underlying material of the dispensingelement body may be any suitable plastic, such as polypropylene which isgenerally rigid but, under impact will plastically deform to a slightdegree. The two materials are therefore of different hardness, but witheach being plastically deformable. The material (e.g., stainless steel)in direct contact with the valve stem tip 60 a is harder than theunderlying material (e.g., plastic). This provides the combined benefitof wear resistance at the direct interface of the valve stem tip 60 aand the valve seat 62, and a damping effect at the underlying, softermaterial. The dispensing element body 52 may be manufactured in a costeffective manner, such as by injection molding. The deformation, asshown in FIG. 7, will be concave and annular when the valve stem tip 60a is convexly curved as shown. This will form an annular concave ring ofdeformation that creates an area of sealing contact between the valvestem tip 60 a and the metal, cone shaped portion 62 a and damps theimpact of the tip 60 a against the metal, cone shaped portion 62 a todecrease atomization of the liquid 15 as it discharges from the outlet64.

FIG. 7A illustrates an alternative embodiment in which all likereference numerals in FIG. 7A, as compared to FIG. 7, refer to likestructure and therefore require no further discussion. In thisembodiment, an outer, plastically deformable layer 63, such as a layerformed of plastic material, is carried on at least the cone-shapedportion 62 a of the valve seat 62. This layer 63 may further extendalong the dispensing tip 62 b. This two-layered construction thereforeallows the dispensing element body 52 a to be formed from a rigidmaterial, such as a metal, if desired. The two-layered construction 62,63 may be formed by using the above-mentioned deep drawing process toform the valve seat 62 from a thin and malleable metal such as stainlesssteel as discussed above. The outer layer 63 may be formed from arelatively rigid plastic, such as polypropylene, that will plasticallydeform to a slight degree, as shown in FIG. 7A, after impact by thevalve stem tip 60 a. The plastic layer 63 may be overmolded onto thevalve seat 62 or adhered to the valve seat 62 in any other suitablemanner. Thus, the result is the same as shown and described inconnection with the embodiment of FIG. 7. Namely, annular concave ringsof deformation 170, 173 will be formed, respectively, in the cone-shapedportion 62 a of the valve seat 62, as well as the underlying plasticmaterial 63. This will damp the impact of the tip 60 a against themetal, cone-shaped portion 62 a to decrease atomization of the liquid 15as it discharges from the outlet 64.

FIGS. 8, 9 and 10 illustrate an alternative embodiment of the dispensingelement in which the valve seat 62 need not deform. In this embodiment,all elements and associated functions that are identical to the previousembodiment are referred to with like reference numerals and, therefore,the same description applies and need not be repeated. Referencenumerals with prime marks (′) correspond to like elements of theprevious embodiment with the same reference numeral, but modified asdescribed. The difference between this embodiment and the previousembodiment is that the dispensing portion 10 a′ includes a valve stem60′ with a valve stem tip 60 a′ that is resilient. Although the valveseat 62 is shown with the same structure as in the first embodiment, itwill be understood that the valve seat may be simplified since it neednot deform and, preferably, does not deform in this embodiment. Thevalve stem tip 60 a′ may be formed from a material that is elastomeric,such as rubber or another polymer. A main portion 61 of the valve stem60′ may be formed from a metal. The valve stem tip 60 a′ may be suitablysecured to the end of the main portion 61, such as by using an adhesiveor over-molding process. One manner of using the valve stem 60′ andelastomeric tip 60 a′ is shown in the process of FIG. 8-10. The valvestem 60′ may initially be spaced from the valve seat 62 and moveddownwardly in the manner previously described such that the valve stemtip 60 a′ deforms into a shape, such as that shown in FIG. 9 as a smallamount of the liquid 15 is forced through the passage 160 and the outlet64. FIG. 10 illustrates a position of the valve stem 60′ in which thetip 60 a′ is in transition and the valve stem 60′ is moving upwardlyduring a dispense cycle. It will be appreciated that while it ispreferred that the valve stem tip 60 or 60′ remain in the closedposition between dispense cycles as previously described to preventleaking, depending on the parameters such as the pressure of the liquid15 and the viscosity of the liquid 15, it may be possible to start thedispense cycle with the valve stem 60 or 60′ in the open position.

While the present invention has been illustrated by a description ofvarious preferred embodiments and while these embodiments have beendescribed in some detail, it is not the intention of the Applicants torestrict or in any way limit the scope of the appended claims to suchdetail. Additional advantages and modifications will readily appear tothose skilled in the art. The various features of the invention may beused alone or in any combination depending on the needs and preferencesof the user. This has been a description of the present invention, alongwith the preferred methods of practicing the present invention ascurrently known. However, the invention itself should only be defined bythe appended claims.

What is claimed is:
 1. A dispenser for applying small amounts of liquidto a substrate, the dispenser comprising: a dispenser body; an actuatorin said dispenser body; and a dispensing element including a dispensingelement body removably coupled to said dispenser body and a valve stemmounted for reciprocating movement within said dispensing element body,said dispensing element body further including a liquid chamber and saidvalve stem including a tip mounted for reciprocating movement withinsaid liquid chamber between open and closed positions, a valve seatengaging said valve stem tip in the closed position, a liquid dispensingoutlet and a liquid supply passage, said valve seat positioned betweensaid liquid chamber and said liquid dispensing outlet, and said liquidsupply passage communicating with said liquid chamber, said valve stemfurther including an opposite end relative to said tip, said oppositeend adapted to be operatively coupled to said actuator when saiddispensing element is coupled to said dispenser body.
 2. The dispenserof claim 1, wherein said dispensing element body further comprises: anair supply passage and an air discharge passage communicating with saidair supply passage, said air discharge passage positioned adjacent tosaid liquid dispensing outlet and adapted to discharge a pressurized aircurtain surrounding the liquid as the liquid is dispensed from saidliquid dispensing outlet.
 3. The dispenser of claim 1, wherein saiddispensing element body further comprises: a connector element adaptedto couple with a container of the liquid.
 4. The dispenser of claim 3,wherein said dispenser body further comprises an opening adapted toreceive an outlet portion of the container, and the connector element ispositioned in said opening when the dispensing element body is coupledto said dispenser body.
 5. The dispenser of claim 1, wherein saiddispensing element is disposable and said dispensing element bodycomprises a plastic material.
 6. The dispenser of claim 5, wherein saidvalve seat includes a portion that is malleable, said portion of saidvalve seat overlying said plastic material and being deformed by saidvalve stem tip in the closed position, said plastic material of saiddispensing element body further being deformable to allow deformation ofsaid valve seat portion, thereby damping impact of the valve stem tipagainst said valve seat and forming an area of sealing contact betweensaid valve stem tip and said valve seat.
 7. The dispenser of claim 6,wherein said valve seat further comprises a cone shaped portion forengaging said valve stem tip and an elongate tip portion including aliquid dispensing passage communicating with said liquid dispensingoutlet.
 8. The dispenser of claim 7, wherein said dispensing elementbody further comprises: an air supply passage and an air dischargepassage communicating with said air supply passage; and a securing capremovably coupled to said dispenser body and securing said dispensingelement to said dispenser body, said securing cap including an openingthat receives said elongate tip portion of said valve seat, said openingcommunicating with said air discharge passage and configured to direct apressurized air curtain surrounding liquid dispensing from said liquiddispensing outlet.
 9. The dispenser of claim 1, wherein said dispensingelement further comprises a dynamic seal engaging said valve stem andpreventing escape of liquid from said liquid chamber, said valve stemextending through said dynamic seal such that said opposite end of saidvalve stem is positioned outwardly of said liquid chamber and intoengagement with said actuator.
 10. The dispenser of claim 9, furthercomprising a spring element coupled with said dispensing element bodyand said valve stem for biasing said opposite end into engagement withsaid actuator.
 11. The dispenser of claim 1, wherein said valve seatincludes a first portion that is malleable and a second portion formedfrom a plastic material, said first and second portions being deformedby said valve stem tip in the closed position thereby damping impact ofthe valve stem tip against said valve seat and forming an area ofsealing contact between said valve stem tip and said valve seat.
 12. Adispenser for applying small amounts of liquid to a substrate, thedispenser comprising: a dispenser body; a valve stem mounted forreciprocating movement within said dispenser body, said dispenser bodyfurther including a liquid chamber and said valve stem including a tipmounted for reciprocating movement within said liquid chamber betweenopen and closed positions; and a valve seat in said dispenser bodyengaging said valve stem tip in the closed position, said valve seatformed by a first material in abutting contact with a second material,said first material positioned for contact with said valve stem tip andbeing of greater hardness than said second material, said first andsecond materials each being plastically deformed when said valve stemmoves to the closed position thereby damping impact of the valve stemtip against said valve seat and forming an area of sealing contactbetween said valve stem tip and said valve seat.
 13. The dispenser ofclaim 12, wherein said first material comprises a metal and said secondmaterial comprises a plastic.
 14. The dispenser of claim 13, whereinsaid valve seat is part of a disposable dispensing element body, andsaid dispensing element body comprises said plastic material.
 15. Thedispenser of claim 13, wherein said valve seat further comprises a coneshaped portion for engaging said valve stem tip and an elongate tipportion including a liquid dispensing passage communicating with saidliquid dispensing outlet.
 16. The dispenser of claim 12, wherein saiddispensing portion further comprises: an air supply passage and an airdischarge passage communicating with said air supply passage, said airdischarge passage positioned adjacent to said liquid dispensing outletand adapted to discharge a pressurized air curtain surrounding theliquid as the liquid is dispensed from said liquid dispensing outlet.17. The dispenser of claim 12, wherein said first material and saidsecond material of said valve seat are adhered to each other to form aunitary structure.
 18. A dispenser for applying small amounts of liquidto a substrate, the dispenser comprising: a dispenser body; a valve stemmounted for reciprocating movement within said dispenser body, saiddispenser body further including a liquid chamber and said valve stemincluding a tip mounted for reciprocating movement within said liquidchamber between open and closed positions; and a valve seat in saiddispenser body engaging said valve stem tip in the closed position;wherein said valve stem tip is formed from a deformable, resilientmaterial, said valve stem tip being deformed against said valve seatwhen said valve stem moves to the closed position thereby damping impactof the valve stem tip against said valve seat and forming an area ofsealing contact between said valve stem tip and said valve seat.
 19. Thedispenser of claim 18, wherein said valve stem further includes a mainportion coupled with said tip, said main portion formed from a rigidmetal and said tip formed from an elastomeric material.
 20. A method ofapplying a small amount of liquid to a substrate during a dispensecycle, the liquid being dispensed from a dispenser including a valvestem with a tip, a liquid chamber, a liquid dispensing passagecommunicating with a liquid dispensing outlet, and a valve seatpositioned between the liquid chamber and the liquid dispensing passage,the method comprising: moving the valve stem tip from a closed positionwhich is engaged with the valve seat to an open position which isdisengaged and spaced from the valve seat; allowing pressurized liquidto flow from the liquid chamber past the valve stem tip and into theliquid dispensing passage; moving the valve stem tip from the openposition to the closed position while dispensing the small amount ofliquid onto the substrate; and maintaining the valve stem tip in theclosed position until an initiation of a subsequent dispense cycle. 21.The method of claim 20, wherein the valve seat is deformed by the valvestem tip as the valve seat is engaged by the valve stem tip in theclosed position.
 22. The method of claim 20, wherein the valve stem tipis deformed by the valve seat as the valve stem tip engages the valveseat in the closed position.
 23. A method of applying a small amount ofliquid to a substrate, the liquid being dispensed from a dispenserincluding a valve stem with a tip, a liquid chamber, a liquid dispensingpassage communicating with a liquid dispensing outlet, and a valve seatpositioned between the liquid chamber and the liquid dispensing passage,the valve seat comprised of first and second plastically deformablematerials having different hardnesses, the method comprising: moving thevalve stem tip from an open position disengaged from the valve seat to aclosed position engaged with the valve seat; and plastically deformingthe first and second materials by impact of the valve stem tip with thevalve seat in the closed position.
 24. The method of claim 23, whereinthe first material comprises a metal, and the second material comprisesa softer material, method further comprising: directly contacting thevalve stem tip with the metal in the closed position, and deforming themetal into the softer material.